The invention relates to thin film batteries and methods of manufacture.
A thin film battery typically comprises a substrate having one or more thin films thereon, which may serve as, for example, current collectors, a cathode, an anode, and an electrolyte, that cooperate to generate a voltage. The thin film batteries typically are less than about {fraction (1/100)}th of the thickness of conventional batteries. The thin films are typically formed by thin film fabrication processes, such as for example, physical or chemical vapor deposition methods (PVD or CVD), oxidation, nitridation or electro-plating. The substrate material is selected to provide good dielectric properties and good mechanical strength. Suitable substrate materials may include for example, oxides such as aluminium oxide and silicon dioxide; metals such as titanium and stainless steel; and semiconductors such as silicon.
However, conventional substrate materials often limit the ability of the battery to store electrical energy to achieve high energy density or specific energy levels. The energy density level is energy level per unit volume of the battery. The specific energy level is the energy level per unit weight of the battery. Conventional batteries typically achieve energy density levels of 200 to 350 Whr/l and specific energy levels of 30 to 120 Whr/l. However, it is desirable to have a thin film battery that provides higher energy density and specific energy levels to provide more power per unit weight or volume.
The ability to achieve higher energy levels is also enhanced by forming a crystalline cathode film on the substrate. The crystalline cathode film can also provide better charging and discharging rates. However, it is difficult to fabricate thin film batteries having crystalline cathode films on the substrate. Typically, the cathode is a thin film deposited on the substrate in the amorphous or microcrystalline form, and thereafter, crystallized by annealing at high temperatures. For example, an amorphous or microcrystalline film of LiCoO2 is typically annealed at about 700xc2x0 C. to obtain a crystalline LiCoO2 cathode film. However, the higher annealing temperature constrains the types of materials that may be used to form the other thin films on the substrate. The other thin film materials should not, for example, soften, melt, oxidize, or inter-diffuse at annealing temperatures. The annealing process may also generate thermal stresses that arise from the difference in thermal expansion coefficient of the substrate, cathode, and current collector, resulting in delamination or peeling off of the thin films or even the entire thin film battery structure. Thus, conventional methods are often deficient in their ability to fabricate the crystalline cathode film of the thin film battery.
Thus it is desirable to have a thin film battery capable of providing relatively high energy density and specific energy levels. It is also desirable to reduce the temperatures of fabrication of the crystalline thin film materials, especially in the fabrication of cathode comprising LiCoO2.
In one aspect, the present invention comprises a battery comprising first and second electrodes on a substrate that is less than 100 microns thick.
In another aspect, the present invention comprises a thin film battery comprising a substrate comprising mica and first and second electrodes on the substrate.
In yet another aspect, the present invention comprises a method of manufacturing a battery comprising forming a substrate comprising mica, and forming one or more films on the substrate to generate or store an electrical charge.
In a further aspect, the present invention comprises a method of making a thin film battery comprising placing a substrate in a chamber having a LiCoO2 target, introducing a process gas into the chamber, energizing the gas by applying a current at a power density level of from about 0.1 to about 20 W/cm2 to the target, and exhausting the gas.
In another aspect, the present invention comprises a sputtering chamber comprising a fixture for holding a substrate, a sputtering target facing the substrate, a gas outlet to provide a gas to the chamber, a pair of electrodes to energize the gas to sputter the target, and a plurality of magnets about the sputtering target, the magnets having different magnetic field strengths.